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In "Instincts and Their Vicissitudes," Freud (1915a) set forth a conceptual scheme that includes all the points required for a satisfactory description and psychological investigation of a drive. We lack such a scheme for the presentation and investigation of an ego mechanism, and do not yet have an accepted procedure we can rely on. However, I will only be following accustomed ways if I start from a biological viewpoint, and in so doing distinguish between the phylogenetic and ontogenetic approaches.
In searching for biological equivalents of isolation one may think of autotomy, which is instanced by the self-amputation of damaged segments observed in worms; this, however, would correspond rather to a combination of isolation and projection. A more appropriate model may be found in segregation, in which undigestible foreign bodies are surrounded by concentrated layers of blood cells and form a nodule, a process followed by encapsulation.
If we take a broader view of isolation we may think of a general biological principle of cell development. In early stages of ontogenetic development cells are first totipotential, then multipotential, and, finally, unipotential; that is to say, cells progressively lose the capacity to form cells of various kinds. A general function splits up into a diversity of special functions. Thus, what was once contained in a unit becomes divided into distinctively isolated partial functions. This gradual isolation of functions is the prerequisite of differentiation; but it may lead under pathological conditions to disastrous results. Analogous situations are observable in the psyche.
Ontogeny can be viewed as a series of separating steps leading to increased isolation, beginning with birth and ending with the final